Santiago Hills Phase II Planned Community and East Orange Planned Community Area 1 Runoff Management Plan Issue Date: 2 May 2005 Santiago Hills Phase II Planned Community and East Runoff Management Plan Orange Planned Community, Area 1 Issue Date: 2, May 20055 VOLUME 1 TABLE OF CONTENTS SECTION 1: INTRODUCTION ..................................................................................................... 1-1 1.1 PROJECT DESCRIPTION........................................................................................... 1-1 1.2 GENERAL OVERVIEW – RUNOFF MANAGEMENT PLAN ....................................... 1-9 SECTION 2: EXISTING WATERSHED AND FLOOD PROTECTION ASSESSMENT .............. 2-1 2.1 BACKGROUND............................................................................................................ 2-1 2.2 FLOODPLAIN MAPPING............................................................................................. 2-1 2.3 WATERSHED DESCRIPTION..................................................................................... 2-3 SECTION 3: REGULATORY REQUIREMENTS AND DESIGN CRITERIA ............................... 3-1 3.1 FLOOD PROTECTION REQUIREMENTS .................................................................. 3-1 3.1.1 BACKBONE SYSTEM ...................................................................................... 3-1 3.1.2 LOCAL SYSTEM .............................................................................................. 3-1 3.2 HYDRAULIC DESIGN.................................................................................................. 3-2 SECTION 4: DESCRIPTION OF EXISTING DRAINAGE FACILITIES ....................................... 4-1 4.1 EXISTING CULVERTS AND STORM DRAIN FACILITIES ......................................... 4-1 4.1.1 ETC FACILITIES............................................................................................... 4-1 4.1.2 IRVINE REGIONAL PARK................................................................................ 4-1 4.1.3 JAMBOREE ROAD........................................................................................... 4-1 4.1.4 CHAPMAN AVENUE / SANTIAGO CANYON ROAD ...................................... 4-2 4.2 EXISTING CHANNEL FACILITIES .............................................................................. 4-2 4.2.1 HANDY CREEK ................................................................................................ 4-2 4.2.2 SANTIAGO CREEK .......................................................................................... 4-3 4.3 EXISTING RESERVOIRS AND FLOOD CONTROL FACILITIES............................... 4-3 4.3.1 PETERS CANYON RESERVOIR..................................................................... 4-3 4.3.2 VILLA PARK FLOOD CONTROL DAM ............................................................ 4-6 4.3.3 CALTRANS BASIN (ETC-1) ............................................................................ 4-6 4.3.4 SANTIAGO RESERVOIR (IRVINE LAKE); SANTIAGO DAM.......................... 4-6 4.4 NATURAL DRAINAGES ............................................................................................ 4-11 4.4.1 NORTH TRIBUTARY...................................................................................... 4-11 4.4.2 SOUTH TRIBUTARY ...................................................................................... 4-11 4.4.3 NATURAL DRAINAGE IN THE ETC-9 WATERSHED................................... 4-11 4.4.4 WOODY’S COVE............................................................................................ 4-11 SECTION 5: WATERSHED HYDROLOGY ................................................................................. 5-1 5.1 SURFACE HYDROLOGY CHARACTERISTICS......................................................... 5-1 5.1.1 PRECIPITATION .............................................................................................. 5-1 5.1.2 SURFACE FLOODING AND FLOW PATHS.................................................... 5-1 5.1.3 WATERSHED CHARACTERISTICS................................................................ 5-3 5.2 WATERSHED MODEL DEVELOPMENT .................................................................... 5-3 5.2.1 WATERSHED PARAMETERS/CHARACTERISTICS...................................... 5-3 RBF Consulting i Prepared by The Irvine Company for Consideration by The City Of Orange Santiago Hills Phase II Planned Community and East Runoff Management Plan Orange Planned Community, Area 1 Issue Date: 2, May 20055 5.2.2 DESIGN RAINFALL .......................................................................................... 5-7 5.2.3 RATIONAL METHOD ....................................................................................... 5-8 5.2.4 UNIT HYDROGRAPH (UH) .............................................................................. 5-9 5.2.5 CONCENTRATION POINTS USED FOR COMPARISON............................. 5-10 5.2.6 DESIGN DISCHARGE METHODS APPLIED TO POINTS 1 THROUGH 6 .. 5-10 5.3 EXISTING BASELINE WATERSHED ANALYSIS ..................................................... 5-11 5.3.1 JAMBOREE ROAD ANALYSIS (POINT 2)..................................................... 5-13 5.3.2 PETERS CANYON RESERVOIR ANALYSIS (POINT 1)............................... 5-14 5.3.3 SANTIAGO RESERVOIR ANALYSIS (POINT 6)........................................... 5-14 5.3.4 IRVINE REGIONAL PARK AREA (POINTS 3, 4, and 5)................................ 5-14 5.4 PROJECT WATERSHED ANALYSIS........................................................................ 5-14 5.5 ULTIMATE CONDITION WATERSHED ANALYSIS.................................................. 5-19 5.6 SANTIAGO CREEK / VILLA PARK DAM IMPACTS ................................................. 5-21 SECTION 6: HYDROLOGIC IMPACTS AND PROJECT DESIGN FEATURES ........................ 6-1 6.1 POINT 1 (NORTH OUTLET FROM PETERS CANYON RESERVOIR TO HANDY CREEK PIPE) ................................................................................................. 6-1 6.1.1 PEAK FLOWS AT THE NORTH OUTLET AFTER DEVELOPMENT .............. 6-2 6.1.2 ADDITIONAL PROJECT DESIGN ALTERNATIVES ....................................... 6-2 6.2 POINT 2 (JAMBOREE ROAD—THE CONFLUENCE OF ALL FLOWS BEFORE THEY ENTER PETERS CANYON RESERVOIR) .................................................... 6-3 6.2.1 PEAK FLOWS DOWNSTREAM FROM THE JAMBOREE CULVERTS.......... 6-3 6.2.2 PROJECT DESIGN FEATURES ...................................................................... 6-4 6.3 POINTS 3 (SANTIAGO CREEK UPSTREAM OF THE IMPROVED IRVINE REGIONAL PARK), 4 (SANTIAGO CREEK DOWNSTREAM OF THE IMPROVED IRVINE REGIONAL PARK AND UPSTREAM OF VILLA PARK RESERVOIR), AND 5 (IMPROVED IRVINE REGIONAL PARK)....................................................... 6-4 6.3.1 PEAK FLOWS AT POINTS 3, 4, AND 5 AFTER DEVELOPMENT.................. 6-5 6.3.2 PROJECT DESIGN FEATURES ...................................................................... 6-5 6.4 POINT 6 (WOODY’S COVE AT IRVINE LAKE)........................................................... 6-6 6.4.1 PEAK FLOWS AT POINT 6 AFTER DEVELOPMENT..................................... 6-6 6.4.2 ADDITIONAL PROJECT DESIGN FEATURES ............................................... 6-7 6.5 POTENTIAL COMBINED IMPACTS............................................................................ 6-7 SECTION 7: HYDRAULICS ......................................................................................................... 7-1 7.1 FLOODPLAIN HYDRAULICS ...................................................................................... 7-1 7.2 STORM DRAIN FACILITIES........................................................................................ 7-6 7.3 PETERS CANYON RESERVOIR HYDRAULICS........................................................ 7-8 SECTION 8: DEBRIS AND SEDIMENT YIELD........................................................................... 8-1 8.1 GENERAL .................................................................................................................... 8-1 8.2 SEDIMENT YIELD ....................................................................................................... 8-3 8.3 SEDIMENT TRANSPORT............................................................................................ 8-4 SECTION 9: STORM WATER DETENTION ............................................................................... 9-1 SECTION 10: STREAM STABILIZATION................................................................................... 10-3 RBF Consulting ii Prepared by The Irvine Company for Consideration by The City Of Orange Santiago Hills Phase II Planned Community and East Runoff Management Plan Orange Planned Community, Area 1 Issue Date: 2, May 20055 SECTION 11: RUNOFF WATER QUALITY ASSESSMENT....................................................... 11-4 11.1 GENERAL .................................................................................................................. 11-4 SECTION 12: DESIGN CONSIDERATIONS ............................................................................... 12-1 12.1 AGENCY AGREEMENTS, PERMITS, AND APPROVALS ....................................... 12-1 12.2 GEOTECHNICAL ....................................................................................................... 12-1 12.3 ENVIRONMENTAL CONSTRAINTS ......................................................................... 12-1 12.4 ULTIMATE DEVELOPMENT REQUIREMENTS ......................................................